The present invention relates in general to mineral mining apparatus and more particularly to a device for limiting or controlling the stroke of a hydraulic ram used in such apparatus.
It is known to employ, in a mineral mining installation, hydraulic shifting rams which connect movable roof supports to a scraper-chain conveyor arranged alongside a mineral face. These rams are extended and retracted alternately from time-to-time to thrust and shift the conveyor forwardly towards the mineral face and to draw up the roof supports to follow this shifting progress. In most cases, the shifting rams are extended and retracted by their full working stroke but under certain conditions it may be necessary to displace the conveyor section or the roof support associated with a ram by a distance somewhat less than the full working stroke of the ram. Use can then be made of a device which serves to limit the stroke of the ram to a distance less than its full stroke. Examples of known types of devices are described in German Pat. Nos. 1226972, 1801564, 2220452 and 2651398. Generally speaking, known stroke limiting devices all have some form of stop physically located between the cylinder of the ram and a head at the end of its piston rod but suffer from certain disadvantages.
A general object of this invention is to provide an improved stroke-limiting device.